I was never able to get HtmlHelper extension methods to work, I always recieved:
'IHtmlHelper' does not contain a definition for 'MethodName' and no extension method 'MethodName' accepting a first argument of type 'IHtmlHelper' could be found (are you missing a using directive or an assembly reference?)
Even though I had the proper namespace in my _ViewImports.cshtml file. So I decided to use the ability of Razor pages to now support injecting services that have been registered for dependency injection. As an example I have the need to inject some values from my configuration file into my _Layout.cshtml file. So I did the following:
1) Defined a IConfigurationHelperService interface:
public interface IConfigurationHelperService
{
string GetApiUrl();
}
2) Defined an implementation of that interface in a ConfigurationHelperSerivce class (which itself is using dependency injection to get the regular configuration class):
public class ConfigurationHelperService : IConfigurationHelperService
{
public ConfigurationHelperService(IConfiguration configuration)
{
Configuration = configuration;
}
private IConfiguration Configuration { get; }
public string GetApiUrl()
{
return GetConfigurationValue(ApiUrl);
}
private string GetConfigurationValue(string key)
{
var value = Configuration[key];
if (value.IsNullOrEmpty()) throw new KeyNotFoundException($"Configruation does not contain an instance of {key}");
return value;
}
}
3) Registered the service for injection via ConfigureServices in Startup.cs:
public void ConfigureServices(IServiceCollection services)
{
services.AddSingleton<IConfigurationHelperService, ConfigurationHelperService>();
services.AddMvc();
}
4) Added the proper namespace as a using statement into my _ViewImports.cshtml file.
5) Used the @inject keyword to define it for use in the _Layout.cshtml file.
@inject IConfigurationHelperService ConfigHelper
<!DOCTYPE html>
<html>
...
@ConfigHelper.GetApiUrl()
...
</html>
It worked great for me, and I can see a lot more uses for this on simpler pages where defining models would be too much work.